Closer to the truth

New evidence suggests it may be relatively easy to transfer DNA material to an individual which is then found at a scene of a felony. New experiments show “touch DNA” where cells are left at a scene of an illegitimate act may in certain circumstances establish little.

The process of “touch DNA” is used by forensics to analyse DNA, it is so called because it only requires small traces of DNA on objects that have been touched, as small as 7 to 10 skin cells. The process is far from assured however with forensic investigators being able to contaminate a felony scene with things like the brushes being used and even cross contamination from other previous cases. The latter may be because DNA may survive any cleaning process and any extracted DNA may originate from multiple sources. Modern DNA analysis may be now so sensitive, contamination from outside sources may be easy and this may lead to investigators focusing on the mistaken individual.

A new study by Cale and colleagues published in the journal of forensic sciences, demonstrates through real life experiments how secondary DNA material may be detected by new DNA detection technology. The team found in some situations all what was necessary was a handshake, cells then were transferred from one individual to another. After contact, individuals partaking in handshakes handled knives which were then analysed using the new technology, the results of the DNA identifiler detected secondary DNA in 85% of the cases. In a small handful of cases the identifiler identified the secondary volunteer as committing the illegitimate act, this was detected even though the individual had an absence of contact with the knife, the real handler of the knife went undetected.

The evidence is an important update to locard’s exchange principle which states an individual may leave DNA traces at the scene of a felony and may also have acquired material from the scene, these are routinely used as a basis in an investigation. This principle originated in the 1930s and with the secondary transfer of DNA first discovered in 1997 a period has passed where police and forensic investigators were unaware and unconcerned about secondary transfer. Previous studies using other detection technology disputed the presence of secondary DNA transfer, this might have been because the technology may have had decreased sensitivity.

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“Most of the articles I’ve read about secondary DNA transfer say, theirs is unable to really have any impact on the end result,” Cale lead author said. The study by Cale and colleagues however, demonstrates how easy foreign DNA may be admitted into a sample. “This is a well designed project. It may change the way the medico legal system looks at DNA evidence.” Said Krista Latham, co-author. Findings in relation to the number of DNA profiles shared on an object, showed that single profile analysis is simple however, analysing multiple DNA sources may be a complex process. This highlights the challenges of assigning a felony to an individual where multiple sources of DNA might be present, may be far from assured evidence.

Overall the findings may show that DNA transferred by an individual to an object might be identified as being the only origin or a significant origin without actually having direct contact with the object. Cale the lead author commented, “Sometimes the only evidence in a case is DNA, and this emphasises that individuals need to interpret the entirety of a case. Even everyday people need to understand that DNA may far from be a magic bullet, it needs to be interpreted like any piece of evidence.” “This research highlights the need to phase out “touch DNA” from forensic vocabulary” said Cale. The outcome from this new research may support more accurate decisions by the legal system to take place and by suggesting a more rigorous process, might be undertaken to arrive at superior conclusions.

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